class_docstr: Class for the Hitting Set Algorithm to obtain a approximate minimal set of backdoor variables
  to condition on for each node pair.
docstr: Obtain count of number of sets each particular node belongs to.
  
  :param set_index: Set of indices to consider for calculating the number of sets "hit" by a variable..
docstr_tok: ["Obtain","count","of","number","of","sets","each","particular","node","belongs","to",".",":","param","set_index",":","Set","of","indices","to","consider","for","calculating","the","number","of","sets","``","hit","''","by","a","variable",".."]
code: def _count_vars(self, set_index=None):
      """
      Obtain count of number of sets each particular node belongs to.
  
      :param set_index: Set of indices to consider for calculating the number of sets "hit" by a variable..
      """
      var_dict = {}
  
      if set_index == None:
          set_index = set([i for i in range(len(self._list_of_sets))])
  
      for idx in set_index:
          s = self._list_of_sets[idx]
  
          for el in s:
              if el not in self._colliders:
                  if el not in var_dict:
                      var_dict[el] = 0
                  var_dict[el] += 1
  
      return var_dict
  
imports: import networkx
  from dowhy.utils.graph_operations import adjacency_matrix_to_adjacency_list
label_desc: Use image node_id 4 for calling the HittingSetAlgorithm obj's underlying member method code with example usage: obj._count_vars(set_index) and returns: var_dict